Thin film recording and method of making

ABSTRACT

A thin film of magnetic recording material is sputter deposited over a base layer of gold and tantalum on a polished substrate. A protective layer of gold and tantalum is deposited overlaying the magnetic recording film. A solid lubricant layer such as carbon, preferably in the form of graphite, gold, silver, tin, molybdenum disulfide, and tungsten disulfide is sputter deposited or ion plated over the protective layer to reduce wear. The recording contacting portion of the recording head is similarly coated with a solid lubricant material. Other suitable protective materials include tantalum, niobium, tungsten and nitrides and carbides of such metals. In a preferred method for making such recording members, the layers are successively sputter deposited in an evacuated sputter chamber, whereby the recording layers and protective coatings are formed in a continuous process requiring only one pump down.

RELATED CASES

This is a division, of application Ser. No. 736,814, filed Oct. 29,1976, U.S. Pat. No. 4,277,540 which in-turn was a continuation-in-partof parent application Ser. No. 139,887 filed May 3, 1971, abandoned.

DESCRIPTION OF THE PRIOR ART

Heretofore, thin film magnetic recording media, such as discs, drums,tapes and the like have been manufactured by plating extremely thinmetallic films of magnetic recording material onto a suitable substratemember. Generally speaking, the metallic magnetic recording materials,such as iron, nickel, cobalt or nickel-cobalt alloys are deposited to athickness between two and ten microinches. Such thin films are subjectto corrosion in storage and use and, thus, corrosion resistantovercoatings have been applied to a thickness of between two and fivemicroinches. Corrosion resistant materials for the coatings haveincluded rhodium, C_(r) O and SiO.

Such thin magnetic films have typically been deposited by a number ofdifferent methods, such as by electrochemical deposition, auto catalyticdeposition, or vacuum deposition by evaporating the magnetic material inan evacuated chamber and condensing the evaporated material on thesubstrate. Various magnetic materials and methods for applying same aredisclosed and discussed in an article entitled "A Critical Review ofMagnetic Recording Materials" appearing in the IEEE Transactions onMagnetics, Volume MAG-5, #4, of December 1969, pages 821-839. And in anarticle entitled "An Analysis of High-Coercivity Thin Film FabricationTechniques and Their Associated Properties" appearing in theNovember-December 1968 issue of Electrochemical Technology, pages419-427.

Briefly, the greatest problem in utilizing thin film magnetic recordingmedia is the susceptibility of magnetic recording media to wear. Thetransducer normally skims between a few microns and several microinchesabove the magnetic media supported by a thin film of compressed air.Periodically the transducer sinks into contact with the recording mediaresulting in a high speed impact of the transducer with the recordingmedia. Collisions of this nature cause extreme wear and actual breakdownand destruction of portions of the recording media. Wear of most thinfilms is usually attributed to the breakdown of adhesion between themetal film and the substrate.

Protective layers deposited over the recording media must be welladhered to the media and have a greater cohesion than the metal film onwhich they are deposited or they will compound the problem. In addition,the overcoated protective layers are preferably conductive to preventthe build up of statis electricity. The use of lubricants to minimizethe problems of wear and impact has not been satisfactory. Suchlubricants often tend to accumulate dust and loose magnetic material onthe disc or tape. Debris collected on the transducer can cause severedamage to the magnetic material in an avalanching effect.

The protective overcoating layers should be corrosion resistive andelectrically conductive to prevent build-up of static electric charge.Evaporated films exhibit by far the worse wear characteristic comparedto electroless and electro plated films, probably due to their porosityand generally poor adhesion to the substrate.

Vacuum deposition is the least complex of the fabrication techniques inthat it is truly a one step process. However, vacuum deposited filmsheretofore have had excess porosity leading to poor wear and corrosionresistance.

Others have attempted to sputter deposit thin films of magneticrecording material onto suitably polished substrates of glass and fusedquartz. However, as reported in U.S. Pat. No. 3,148,079 issued Sept. 8,1964, such prior attempts at sputter depositing magnetic films has notbeen successful.

SUMMARY OF THE PRESENT INVENTION

The principal object of the present invention is the provision of animproved thin film magnetic recording medium and method of making same.

In one feature of the present invention, the magnetic recording film iscovered with a protective coating of gold and tantalum, whereby aprotective coating is formed on the magnetic recording film.

In another feature of the present invention, a wear resistant layer ofcarbon is deposited as by sputtering on ion plating, preferably in theform of graphite, over the thin film of magnetic recording material toprotect it from excessive wear.

In another feature of the present invention, the surface portion of themagnetic transducer which occasionally contacts the recording medium iscoated with an adherent solid lubricant layer of carbon preferably inthe form of graphite.

In another feature of the present invention, one or more of the layersof the recording medium such as the magnetic recording material, or oneor more of its protective coatings, is deposited overlaying a polishedsurface of the substrate by sputter depositing the respective materialover the substrate in a gaseous atmosphere at subatmospheric pressure.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A suitable substrate material such as mylar, in the case of recordingtape, or aluminum, alumina, beryllia, or glass such as pyroceram, pyrexor the like, is lapped and polished to provide an extremely smoothsurface onto which the recording medium is to be deposited. Thesubstrate member is disposed in a chamber which is evacuated to arelatively low pressure, as of 5×10⁻⁵ torr. Suitable diffusion pumpsand/or getter ion pumps together with liquid nitrogen forepumps andtraps are utilized for the pump down of the chamber to assure a cleanvacuum and to prevent back streaming of oil from the diffusion pumps. Aquartz heating element is placed within the chamber to provide a mildbakeout of the substrate during pump down. After the pressure reaches5×10⁻⁵ torr the quartz heaters are turned off and argon is leaked intothe chamber through an automatic leak valve to obtain a pressure of7×10⁻³ torr.

The evacuated chamber contains any one of a number of different rfinduced plasma sputtering electrode arrangements, such as any one ormore of those disclosed in an article entitled "Advances In RF-InducedPlasma Sputtering" appearing in SCP and Solid-State Technology,December, 1967, pages 45-49 and 75. In a preferred embodiment, a plasmacoil configuration of the electrodes is employed. Such configuration ofelectrodes includes a pair of target electrodes made of a material whichis to be sputtered onto the substrate. A dc bias potential is applied tothe target electrodes. Radio frequency energy is applied to a coilinterposed between the target electrodes and the substrate. The dc powersupply is used to establish a target potential which is negative withrespect to the glow discharge.

In the glow discharge, argon ions are created and they are attractedfrom the plasma to bombard the target electrodes. The ion bombardment ofthe target electrodes causes the target material to be sputteredtherefrom and to be collected or deposited upon the substrate which isto be coated. The sputtered target material arrives at the substratewith energies between 30 and 300 electron volts. By causing the targetmaterial to be driven onto the substrate, improved density of thedeposited layer and improved adhesion between the deposited layer andthe substrate or sublayer is obtained. Both of these characteristics,namely the improvement in density of the layer and of the improvedadhesion of the layer to the substrate improves the wear resistance ofthe resultant recording medium.

A base layer of material (primary coat) which is compatible with thesubstrate is deposited up to 40 microinches in thickness, preferably inthe range of 2 to 10 microinches in thickness. The base metal isselected from the group consisting of molybdenum, titanium, chromium,niobium, tantalum, vanadium and tungsten, and is preferably sputterdeposited onto the polished surface of the substrate member. Duringdeposition, relative movement between the substrate and the targets isobtained, as by combined rotation and rectilinear translation of thesubstrate, to assure uniform deposition of the sputtered material ontothe substrate layer. The substrate is preferably first cleaned beforedepositing the base layer by sputter etching the surface, i.e. reversingthe d.c. bias potential such that the substrate becomes the target.

The magnetic recording layer is deposited over the base layer. In apreferred embodiment, target electrodes of magnetic material aresubstituted for the original targets, as by flipping over the targets orby using other targets, for depositing a thin film of magnetic recordingmaterial onto the base layer. For example, a suitable magnetic materialis selected from the class consisting of iron, nickel, cobalt or alloysthereof. In a preferred embodiment a nickel-cobalt alloy consisting of30% nickel and 70% cobalt is sputter deposited onto the base layer to athickness of between 2 and 15 microinches and preferably to a thicknessof approximately 5 microinches. Relative movement between the target andthe substrate is produced, as aforedescribed, to obtain uniformthickness of the deposited layer over the surface to be coated.Alternatively, the magnetic layer is deposited by the conventionalelectroless process.

A corrosion resistant protective layer is deposited, preferably bysputtering, over the magnetic layer to a thickness between 2 and 10microinches and preferably approximately 5 microinches. Suitablecorrosion resistant materials include gold, tantalum, niobium, platinum,chromium, tungsten and rhodium.

However, a corrosion resistant layer of gold and tantalum, preferablyobtained by co-sputter deposition, is especially effective in preventingcorrosion products from permeating the gold and tantalum layer into themagnetic material. The precise mechanism of how gold and tantalum servesto especially inhibit corrosion and corrosion products from diffusionthrough the layer to the substrate is not understood. The tantalum formsa very hard tightly adherent wear resistant and corrosion resistantlayer on the magnetic layer. Gold infiltrates into the grain boundariesto inhibit permeation by corrosion products, such as hydrogen. Gold alsoserves as a solid lubricant on the outer surface of the gold andtantalum layer. Sputter deposited gold, as a solid lubricant, hasincreased adhesion to the tantalum and magnetic layers, thereby reducingthe tendency for the gold to agglomerate on the surface of the recordingmedium.

A tantalum or tantalum and gold base layer (primary coat) is especiallyadvantageous with use of a tantalum or tantalum and gold protectivecoating since such a base layer protects the magnetic layer fromcorrosion products diffusing from the substrate into the magnetic layer.

Alternatively, a corrosion resistant and wear resistant protectivecoating is obtained by reactively sputter depositing refractory nitridesor refractory carbides, such as nitrides or carbides of Si, Zr, Hf, Ti,Ta, W and Nb to a thickness of between two and ten microinches,preferably four microinches, onto the sputter etched or cleaned magneticlayer and then stabilizing the protective layer by growing an anodicoxide layer thereon to a thickness of approximately one to twomicroinches and annealing same at 250°-400° C. for five hours. Suchcarbide and nitride tantalum and niobium layers are anodized by anaqueous solution of 0.1% H₃ PO₄. Such refractory nitrides and carbidesare obtained by introducing N₂ or ethane or methane into the argon glowdischarge used to sputter deposit the other constituents of the nitrideor carbide. See Electrochemical Technology, July-August, 1968 issue,pages 269 et seq. Tungsten carbide reactively sputter deposited, asabovedescribed, also provides a wear resistant coating.

As aforementioned, gold provides a solid lubricant for reducing frictionand thus wear. Other solid lubricants include silver, carbon (especiallyin the form of graphite), M_(o) S₂, Sn and WS₂. Such lubricants arepreferably sputter deposited to a thickness of one to five microinchesover the aforedescribed protective layer. Sputter deposition of thelubricants serves to improve the adhesion of the lubricant to thesublayer, thereby increasing the wear resistance of the protectivecoatings. Of the solid lubricants, gold and graphite are particularlydesirable. Graphite and carbon are particularly suitable for depositionon sublayers comprised of carbide formers such as Si, Zr, Hf, Ti, Ta, Nband W.

The magnetic transducer head portion which occasionally sinks intocontact with the recording medium is preferably formed of or coated withcarbon, preferably in the form of graphite, to provide a low frictionwear resistant contacting surface with the recording medium.

As an alternative to sputter depositing the carbon onto the sublayer,the low friction carbon layer may be formed by ion plating according tothe method disclosed in U.S. Pat. Nos. 3,329,601 or 3,386,909. The useof sputter deposition or ion plating of the carbon coating results in atightly adherent coating of the carbon on the surface coated.

The advantage to the use of sputter deposition for depositing thesuccessive layers of materials onto the substrate member of therecording medium is that such layers may be deposited in a one-stepmethod where the recording medium need only be subjected to one pumpdown within the evacuated chamber. In addition, use of sputterdeposition aparatus allows the substrate surfaces and the surfaces ofsubsequent layers which are to be coated to be cleaned first bybombarding the surface to be coated with ions for cleaning awaycontaminants that may be present on the surface to be coated. In thismanner tightly adherent wear resistant and relatively non porouscoatings are obtained.

What is claimed is:
 1. In a magnetic recording medium, a substratemember, a film of magnetic recording material overlaying said substrate,and a protective layer of gold and tantalum overlaying said film ofmagnetic recording material.
 2. The recording medium of claim 1including a lubricant layer of carbon overlaying said protective layer.3. The recording medium of claim 2 wherein said layer of carbon is inthe form of graphite.
 4. The recording medium of claim 2 wherein saidlayer of carbon is bonded to the adjacent sublayer on said substratemember.
 5. The recording medium of claim 1 wherein said substrate ismade of a material selected from the class consisting of ceramic,aluminum, and glass, said substrate having a polished surface, andwherein said magnetic film is deposited to a thickness between 2 and 15microinches overlaying said polished surface of said substrate.
 6. In amethod for making a magnetic recording medium, depositing a film ofmagnetic recording material onto a substrate member, and depositing alayer of gold and tantalum over said film of magnetic recordingmaterial.
 7. The method of claim 6 wherein said layer of gold andtantalum is deposited by sputtering gold and tantalum over said magneticfilm in a gaseous atmosphere at subatmospheric pressure.
 8. The methodof claim 6 including the step of, depositing a layer of carbon over saidlayer of gold and tantalum.
 9. The method of claim 8 wherein said layerof carbon is deposited by sputtering carbon over said gold and tantalumin a gaseous atmosphere at subatmospheric pressure.
 10. The method ofclaim 9 wherein said carbon is sputtered from a graphite target by ionbombardment to form a graphite layer of carbon over said gold andtantalum.
 11. The method of claim 8 wherein said layer of carbon isdeposited by ion plating carbon over said gold and tantalum layer from aglow discharge in a gaseous atmosphere at subatmospheric pressure. 12.In a method for making a magnetic recording medium the steps of,depositing at subatmospheric pressure a base layer of a metal selectedfrom the group consisting of molybdenum, titanium, chromium, niobium,tantalum, vanadium, and tungsten overlaying a substrate member, saidsubstrate member comprising a material selected from the classconsisting of ceramic, aluminum and glass, depositing at subatmosphericpressure a film of magnetic recording material over said first layer,and depositing at subatmospheric pressure a protective layer of materialselected from the class consisting of niobium, tantalum, and tungstenover said magnetic recording film.
 13. The method of claim 12 includingthe step of forming a solid lubricating layer selected from the classconsisting of carbon, graphite, molybdenum disulfide, tin, gold, silver,and tungsten disulfide over said protective layer.
 14. The method ofclaim 13 wherein said base, magnetic, protective, and lubricating layersare all deposited by sputtering said respective materials onto saidsubstrate from respective targets in a gaseous atmosphere atsubatmospheric pressure.
 15. The method of claim 12 wherein said base,magnetic, and protective layers are all deposited by sputtering saidrespective materials onto said substrate from respective targets in agaseous atmosphere at subatmospheric pressure.
 16. The method of claim12 wherein said step of depositing a protective layer comprises the stepof depositing a layer of gold and tantalum over said magnetic recordinglayer with the proportion of gold in the layer increasing in a directiontaken away from the direction of the magnetic recording layer, wherebythe proportion of gold increases at the outer surface to form alubricating coating over a wear resistant and corrosion resistantprotective layer.
 17. The method of claim 12 wherein each of said baseand protective layers comprises a layer of gold and tantalum.
 18. In amethod for making a recording medium, the steps of, growing a film ofrecording material onto a substrate member, and growing a protectivelayer of material over said film of recording material, such protectivelayer being selected from the class consisting of niobium, tantalum,tungsten, refractory carbides and refractory nitrides.
 19. The method ofclaim 18 including the step of anodizing the protective layer.
 20. Themethod of claim 18 wherein the step of growing the protective layercomprises the step of sputter depositing said protective layer.
 21. Theproduct made by the method of claim
 18. 22. The method of claim 18wherein said protective layer is selected from the group consisting ofsilicon nitride and silicon carbide.